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Beyond the Bale : September 2015
ON FARM 33 The worm population in the sheep and on a pasture (where these sheep have grazed for some time) will have about the same proportion of drench-resistant worms -- the actual proportion will depend on your farm's drench history. But after drenching, the sheep will only contain drench-resistant worms. Their eggs will be the only ones contaminating the pasture for three weeks, at least. If there are worms from the pre-drench population in refugia -- in this paddock or another paddock, in some sheep within this mob or another mob -- then they can be used to dilute the numbers of drench-resistant worms (and the eggs they produce) that have survived in drenched sheep. If used effectively, this prevents these small populations of drench-resistant worms from quickly becoming the main population on your farm. WHAT IS IMPORTANT WHEN USING REFUGIA? Maintaining worms in refugia to dilute numbers of drench-resistant worms also means more worms to infect sheep after drenching. However, with some understanding of when and how to use refugia, you can achieve both good worm control and slower development of drench resistance. 1.Understand the seasonal environmental pattern that influences worm larval development and survival to know when refugia management is most important in your region. • In regions with regular rainfall, short periods of hot and dry or cold, or where perennial pastures persist through hot summer months, there is almost year- round development and survival of larvae on pasture, which will be in refugia. Here, there is less need for deliberate management to maintain worms in refugia. • In regions with regular and prolonged periods of dry, or very hot or very cold weather, larvae will not develop or survive during these times. Here, the proportion of worms on pasture in refugia falls to very low levels and strategies to maintain worms in refugia are especially important. • The key factors in development of eggs to larvae are temperature and rainfall at the time eggs are deposited on the pasture, as well as some weeks after. 2. Distinguish between the worm species. • Refugia strategies are most applicable for scour worms. They need to be applied with more caution where and when barber's pole worm is a major risk. 3. Apply refugia strategies in sheep best able to tolerate worms. • Adult sheep in good body condition are the best class when you are going to leave a proportion undrenched. • Do not apply refugia strategies with lambs, weaners and hoggets. The worms in a local population that are not exposed to a drench are described as being 'in refugia'. If you need to drench into clean paddocks or drench during periods of little or no worm activity, then maintaining worms in refugia provides a powerful and relatively simple way to manage drench resistance. 4. Monitor worm egg counts • Use a WormTest in flocks when you are using refugia strategies to check that excessive worm burdens don't develop. 5. Know your recent drench history. • Drench resistance is specific to a drench group (or active family) and to a particular worm species. Benefits from worms in refugia rely on them being the same species and susceptible to the same drench that was just used. To find practical strategies for using refugia to assist you in the management of drench resistance, look in your regional WormBoss Program at www.wormboss.com.au. The WormBoss website also provides a number of other ways to manage drench resistance. MORE INFORMATION www.wormboss.com.au Like ParaBoss on Facebook at www.facebook.com/paraboss.com.au Lewis Kahn, ParaBoss Executive Officer, 02 6773 2997, lewis paraboss.com.au